/*
** $Id: lgc.h $
** Garbage Collector
** See Copyright Notice in lua.h
*/

#ifndef lgc_h
#define lgc_h

#include "lobject.h"
#include "lstate.h"

/*
** Collectable objects may have one of three colors: white, which means
** the object is not marked; gray, which means the object is marked, but
** its references may be not marked; and black, which means that the
** object and all its references are marked.  The main invariant of the
** garbage collector, while marking objects, is that a black object can
** never point to a white one. Moreover, any gray object must be in a
** "gray list" (gray, grayagain, weak, allweak, ephemeron) so that it
** can be visited again before finishing the collection cycle. (Open
** upvalues are an exception to this rule.)  These lists have no meaning
** when the invariant is not being enforced (e.g., sweep phase).
*/

/*
** Possible states of the Garbage Collector
*/
#define GCSpropagate   0
#define GCSenteratomic 1
#define GCSatomic      2
#define GCSswpallgc    3
#define GCSswpfinobj   4
#define GCSswptobefnz  5
#define GCSswpend      6
#define GCScallfin     7
#define GCSpause       8

#define issweepphase(g) \
    (GCSswpallgc <= (g)->gcstate && (g)->gcstate <= GCSswpend)

/*
** macro to tell when main invariant (white objects cannot point to black
** ones) must be kept. During a collection, the sweep
** phase may break the invariant, as objects turned white may point to
** still-black objects. The invariant is restored when sweep ends and
** all objects are white again.
*/

#define keepinvariant(g) ((g)->gcstate <= GCSatomic)

/*
** some useful bit tricks
*/
#define resetbits(x, m)  ((x) &= cast_byte(~(m)))
#define setbits(x, m)    ((x) |= (m))
#define testbits(x, m)   ((x) & (m))
#define bitmask(b)       (1 << (b))
#define bit2mask(b1, b2) (bitmask(b1) | bitmask(b2))
#define l_setbit(x, b)   setbits(x, bitmask(b))
#define resetbit(x, b)   resetbits(x, bitmask(b))
#define testbit(x, b)    testbits(x, bitmask(b))

/*
** Layout for bit use in 'marked' field. First three bits are
** used for object "age" in generational mode. Last bit is used
** by tests.
*/
#define WHITE0BIT        3 /* object is white (type 0) */
#define WHITE1BIT        4 /* object is white (type 1) */
#define BLACKBIT         5 /* object is black */
#define FINALIZEDBIT     6 /* object has been marked for finalization */

#define TESTBIT          7

#define WHITEBITS        bit2mask(WHITE0BIT, WHITE1BIT)

#define iswhite(x)       testbits((x)->marked, WHITEBITS)
#define isblack(x)       testbit((x)->marked, BLACKBIT)
#define isgray(x)        /* neither white nor black */ \
    (!testbits((x)->marked, WHITEBITS | bitmask(BLACKBIT)))

#define tofinalize(x)  testbit((x)->marked, FINALIZEDBIT)

#define otherwhite(g)  ((g)->currentwhite ^ WHITEBITS)
#define isdeadm(ow, m) ((m) & (ow))
#define isdead(g, v)   isdeadm(otherwhite(g), (v)->marked)

#define changewhite(x) ((x)->marked ^= WHITEBITS)
#define nw2black(x) \
    check_exp(!iswhite(x), l_setbit((x)->marked, BLACKBIT))

#define luaC_white(g) cast_byte((g)->currentwhite &WHITEBITS)

/* object age in generational mode */
#define G_NEW         0 /* created in current cycle */
#define G_SURVIVAL    1 /* created in previous cycle */
#define G_OLD0        2 /* marked old by frw. barrier in this cycle */
#define G_OLD1        3 /* first full cycle as old */
#define G_OLD         4 /* really old object (not to be visited) */
#define G_TOUCHED1    5 /* old object touched this cycle */
#define G_TOUCHED2    6 /* old object touched in previous cycle */

#define AGEBITS       7 /* all age bits (111) */

#define getage(o)     ((o)->marked & AGEBITS)
#define setage(o, a)  ((o)->marked = cast_byte(((o)->marked & (~AGEBITS)) | a))
#define isold(o)      (getage(o) > G_SURVIVAL)

#define changeage(o, f, t) \
    check_exp(getage(o) == (f), (o)->marked ^= ((f) ^ (t)))

/* Default Values for GC parameters */
#define LUAI_GENMAJORMUL  100
#define LUAI_GENMINORMUL  20

/* wait memory to double before starting new cycle */
#define LUAI_GCPAUSE      200

/*
** some gc parameters are stored divided by 4 to allow a maximum value
** up to 1023 in a 'lu_byte'.
*/
#define getgcparam(p)     ((p)*4)
#define setgcparam(p, v)  ((p) = (v) / 4)

#define LUAI_GCMUL        100

/* how much to allocate before next GC step (log2) */
#define LUAI_GCSTEPSIZE   13 /* 8 KB */

/*
** Check whether the declared GC mode is generational. While in
** generational mode, the collector can go temporarily to incremental
** mode to improve performance. This is signaled by 'g->lastatomic != 0'.
*/
#define isdecGCmodegen(g) (g->gckind == KGC_GEN || g->lastatomic != 0)

/*
** Control when GC is running:
*/
#define GCSTPUSR          1 /* bit true when GC stopped by user */
#define GCSTPGC           2 /* bit true when GC stopped by itself */
#define GCSTPCLS          4 /* bit true when closing Lua state */
#define gcrunning(g)      ((g)->gcstp == 0)

/*
** Does one step of collection when debt becomes positive. 'pre'/'pos'
** allows some adjustments to be done only when needed. macro
** 'condchangemem' is used only for heavy tests (forcing a full
** GC cycle on every opportunity)
*/
#define luaC_condGC(L, pre, pos)    \
    {                               \
        if (G(L)->GCdebt > 0) {     \
            pre;                    \
            luaC_step(L);           \
            pos;                    \
        };                          \
        condchangemem(L, pre, pos); \
    }

/* more often than not, 'pre'/'pos' are empty */
#define luaC_checkGC(L)       luaC_condGC(L, (void)0, (void)0)

#define luaC_barrier(L, p, v) (                               \
    (iscollectable(v) && isblack(p) && iswhite(gcvalue(v))) ? \
        luaC_barrier_(L, obj2gco(p), gcvalue(v)) :            \
        cast_void(0))

#define luaC_barrierback(L, p, v) (                           \
    (iscollectable(v) && isblack(p) && iswhite(gcvalue(v))) ? \
        luaC_barrierback_(L, p) :                             \
        cast_void(0))

#define luaC_objbarrier(L, p, o) (                 \
    (isblack(p) && iswhite(o)) ?                   \
        luaC_barrier_(L, obj2gco(p), obj2gco(o)) : \
        cast_void(0))

LUAI_FUNC void luaC_fix(lua_State *L, GCObject *o);
LUAI_FUNC void luaC_freeallobjects(lua_State *L);
LUAI_FUNC void luaC_step(lua_State *L);
LUAI_FUNC void luaC_runtilstate(lua_State *L, int statesmask);
LUAI_FUNC void luaC_fullgc(lua_State *L, int isemergency);
LUAI_FUNC GCObject *luaC_newobj(lua_State *L, int tt, size_t sz);
LUAI_FUNC void luaC_barrier_(lua_State *L, GCObject *o, GCObject *v);
LUAI_FUNC void luaC_barrierback_(lua_State *L, GCObject *o);
LUAI_FUNC void luaC_checkfinalizer(lua_State *L, GCObject *o, Table *mt);
LUAI_FUNC void luaC_changemode(lua_State *L, int newmode);

#endif
